In vitro and in vivo antibacterial effects of indole-3-lactic acid against Salmonella enterica serovar Typhimurium

Salmonella is a prevalent foodborne pathogen that poses a significant threat to public health. Our previous study identified Lactiplantibacillus plantarum ZJ316, a strain known for its production of indole-3-lactic acid (ILA), which exhibits a broad-spectrum bacteriostatic effect. This study aimed to explore the inhibitory mechanism of ILA against Salmonella enterica subsp. enterica serovar Typhimurium ATCC 14028 ( S . Typhimurium) both in vitro and in vivo , as well as to assess its potential to alleviate colitis induced by S . Typhimurium. In vitro experiments revealed that ILA exerts its ant- Salmonella effect by disrupting the transmembrane proton motive force (PMF) and influencing intracellular ATP synthesis. Subsequent experiments conducted in female C57BL/6 mice demonstrated that oral administration of 45.00 mg/L ILA for 21 d effectively reduced S. Typhimurium infection-induced upregulation of pro-inflammatory cytokines (IL-1β and CXCL15; P < 0.01 and P < 0.05, respectively), while promoting the production of anti-inflammatory cytokines (IL-10 and IL-22; P < 0.001). Compared to the control group, the ILA group had a 4.15% increase in the relative abundance of Firmicutes and a 3.95% decrease in Bacteroidota. Furthermore, ILA also effectively countered the reduction of short-chain fatty acids (SCFAs) such as acetic acid and propionic acid caused by S . Typhimurium. These findings indicate that ILA may possess the capability to suppress pathogens, enhance intestinal microecology, and facilitate the repair of intestinal tissue damage.